Device for focusing photographic cameras.



PATENTED MAY 5, 1908.

W. THORNER. DEVICE FOR FOGUSING PHOTOGRAPHIG CAMERAS.

APPLICATION FILED OUT. 9,1906.

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qawd @M PATENTED MAY 5, 1908.

W. THORNER. DEVICE FOR FOGUSING PHOTOGRAPHIG CAMERAS.

I APPLICATION FILED 0019,1906.

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WALTHER TI-IORNER, OF BERLIN, GERMANY.

DEVICE FOR FOCUSING PHOTOGRAPHIC CAMERAS.

Specification of Letters Patent.

Patented May 5, 1908.

Application filed October 9, 1206. Serial No. 338,120.

' tographic Cameras, of which the following is a specification.

My invention relates to a device for focusing photographic cameraswithout using a plate of ground glass. In order to secure this result Iconstruct the focusing device in such a manner that it produces imagesof the objects upon which it is directed, which are more or lessdisplaced with relation to each other or coincide, the degree ofdisplacement depending upon the distance of the objects from thefocusing device. The elements of the focusing device are arranged forrectilinear movement towards each other, such movement enablingcoincidence of the images of objects at varying distances to be secured.This construction of the focusing device allows the focusing of theobjective lens of the camera for objects at varying distances providedthat the objective of the camera is moved with relation to the imagecarrying frame of the camera in accordance with the rectilinear movementof the elements of the focusing device towards each other.

The focusing of the objective lens of the camera is obtained in a verysimple manner by directly connecting one element of the focusing deviceto the objective and the other to the image carrying frame of thecamera. In this instance no coupling means for communicating themovement of the elements of the focusing device to the elements of thecamera are necessary. Of course this embodiment of invention requires aspecial construction of the elements of the focusing device dependingupon the nature of the ob- I jective of the camera.

For the purpose of practically carrying out the invention two images ofthe object for which the objective of the camera is to be focused areproduced by reflecting or refracting spherical surfaces which are arranged at the ends of a base-line and which cooperate with an opticalelement adapted to bring these images into coincidence on rectilinearmovement towards the image producing elements, the length and thedirection of the rectilinear movement being either equal cipalembodiment of the invention.

or in a definite proportion to the movement of the objective of thecamera necessary for focusing the objective for the distance of theobject in question.

The new focusing device is represented on the annexed drawingdiagrammatically in four modifications.

Figures 1 and 2 represent diagrammatically a plan and a vertical sectionof the prin- Fig. 3 shows the images which are used for the adjustmentof the device. Fig. 4 is an axial section through a photographic camerawith a modification of the new focusing device. Fig. 5 is a plan of acamera with a further modification of the focusing device. Fig. 6 showsdiagrammatically a further modification of the focusing devicecomprising the combination of an object glass forming the imageproducing element with two halves of a convex lens forming the imagedisplacing element. Fig. 7 is an end view of the two halves of a convexlens forming the image displacing element of the focusing devicerepresented in Fig. 6. Fig. 8 is an end view of a modified form of theimage displacing element shown in Figs. 6 and 7. Fig. 9 shows a sideelevation of a further modified form of the focusing device. Fig. 10 isa perspective view of a camera provided with a focusing device with thearrangement of the optical elements diagrammatically shown in v Figs. 1and 2;

In the embodiment of the invention represented in Figs. 1, 2 and 10 twosmall concave mirrors I and II are fixed 011 the outside of the camera.Preferably these two mirrors have a diameter of 23 cm. and about thesame focal length as the objective of the camera and are locatedsubstantially in the plane of the sensitive sheet on which the image isto be produced by the objective of the camera. The mirrors I and II arefixed on a narrow ledge X. A third concave mirror III, having a diameterof about 4. cm. is arranged in the same height as the mirrors I and IIand is firmly connected to the objective of the camera so that it ismoved towards the mirrors I and II when the objective is moved towardsthe image plane. The mirror III consists of two halves which are locatedone above the other, with the reflecting surfaces at an angle with eachother so that the one half has substantially the same direction as themirror I and the other the direction of the mirror II. The focal lengthof these two parts of the mirror III is about one half of the focallength of the objective of the camera.

In the case of the construction represented in Fig. 2 the mirrors I, IIand III are arranged at the rear side of the guiding board for theobjective so that on using the camera the obj ective is suspended on itsguiding board, the latter being located at the top end of the camera.

An observer viewing the mirror III from 0 (Fig. 1) or through theopening 0 between the two mirrors I and II when using the embodimentshown in Fig. 10 now sees in the top-half of the mirror III the image ofthe objects projected thereon from I and in the bottom half the ima eprojected thereon from II. The mirror III is arranged at such a distancefrom the mirrors I and II that when focusing the camera for an infinitedistance, an infinitely remote perpendicular line appears to runcontinuously in the top and bottom halves of the mirror III. Each lessdistant perpendicular line appears however to be broken off and the twohalves are wider apart, the closer the object is. If however the lens ismoved away from the sensitive plate, and at the same time, the mirrorIII from the mirrors I and II, an infinitely remote perpendicular linewill now appear to be broken oil, while the image of a less distantperpendicular line is continuous, the coincidence of the two images ofthe same object always taking place, provided that the device isaccurately adjusted, when the image is simultaneously focused on theground glass plate. That which applies to the perpendicular lines alsoapplies to any other line which intersects the dividing line in themiddle of mirror III except that the relative displacement of bothpartial lines is not so great. The focusing is not possible on lineswhich run parallel with the dividing line on III, as such lines onlyappear to run into each other. If an object only consists of horizontallines, the camera would have to be turned in order to be able to focuswith the mechanism.

Fig. 3 shows the focusing of 3 differently remote trees. The apparatusis in focus for the tree 2, while the tree 1 is in front of and the tree3 behind the accurately focused tree.

The focusing of an object is effected in a very simple manner in thatthe lens is moved until the object to be photographed appears continuouswith the top and bottom halves of the mirror III.

Instead of providing two concave mirrors I and II separatedfrom eachother, the mirrors may be ground as parts of one single concave body, asshown in dotted lines in Fig. 1 the part Z between the mirrors I and IIforming one piece together with the said mirrors. This construction isadvisable in so far as the adjustment of the mirrors with relation toeach other is dispensed with. If this construction is used the half ofthe radius of curvature must be equal to of the focal length of theobjective, as can be found by calculation.

The whole focusing system may also be carried out in such a manner thatprismatic convex lenses are employed instead of the inclined concavemirrors. The two image forming lenses must then be in the plane of thelens and the divided lenses uniting the image be in the plane of thesensitive plate. This construction is somewhat more awkward than thatwith concave mirrors but has a the advantage that it yields accurateresults for all ranges provided that the front focal points of thefocusing lenses are located with that of the lens or object glass of thecamera in the same plane perpendicular to the optic axis.

If concave mirrors are used as in the embodiment of inventionrepresented in Figs. 1 and 2 a certain incorrectness is caused by thefact that the concave mirrors are lying behind the objective. Thisincorrectness, it is true, is insignificant if the objects for which theobjective is to be focused are in a distance of more than 8 focallengths. But it would be of practical influence if the distance of theobjects is less than S focal lengths of the ob jective.

If it is not necessary to focus the image after the holder of thephotographic plate has been inserted in the camera, for instance, inlarger camera stands, the two image producing lenses I and II (Fig. 4)may be arranged on each side of and close to the lens or object glassand the lens III taking up the image may be replaced by the ground glassplate. The lenses I and II must then of course be covered beforeexposing the plate. An embodiment of this kind is represented in Fig. 4.

If lenses are used instead of concave mirrors in consequence of theprismatic effect of such lenses the images produced by the focusingdevice show colored edges, unless achromatic lenses or prisms are used.This imperfection is avoided. in the construction represented in Fig. 5showing plane mirrors I and II and convex lenses I and II, the

combination of the mirror I and the lens I forming a substitute for theprismatic lens I of Fig. 4 and the plane mirror IP- and the convex lensII forming in combination a substitute for the prismatic lens II of Fig.4.

The focal length of each of the lenses 1 and II must be equal to thefocal length of the objective of the camera multiplied by M5 if it isdesired that the image is formed in the plane of the body III.

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If one does not require high sensibility of i the focusing device oneneeds only a short base-line. So it becomes possible to use the twohalves of the ob ective of the camera as optical end-points of thebaseline. This arrangement is represented in Fig. 6 of the drawing. Inthis instance the body III consists of a convex lens which is out intotwo pieces which are shifted with relation to each other as shown inFig. 7 the center being designated M. In this instance the body IIIconsisting of two halves of a convex lens shifted with relation to eachother may be cemented to the middle of the ground glass plate. Thisconstruction affords the advantage over the usual focusing of theobjective by producing an image on the ground glass plate that is veryluminous and can be adjusted without a dark-colored cloth.

In view of the fact that the object glass of the camera is symmetricalto the optical axis, it is possible to compose the device in the groundglass plate of a plurality of lens sections having their centers shiftedwith relation to each other. A modification of this kind with four lenssections is represented in Fig. 8, the centers of the lens sectionsbeing again marked M.

Forflner adjustment it is advisable to use a magnifying glass for thecontemplation of the optical element III of the focusing device suchmagnifying glass in the case of Figs. 1, 5 and 6 could. be arranged atO.

The optical element III in the construction of Figs. 7 and 8 could alsobe constructed by itself or in connection with a magnifying device as afocusing device separated from the photographic camera which in use isput on an opening in the rear-wall of the camera. This form of focusingdevice is represented in Fig. 9 in which the letter a designates amagnifying convex-lens and the letter I), the body causing the images ofob jects at definite distances produced by different parts of the objectglass to coincide, and at the same time a shifting of the images ofobjects at different distances with relation to each other.

I have shown and described the best means now known to me of embodyingmy invention without intending to limit myself to the exactconstructions as described and shown except as required by the scope ofthe ap pended claims.

My new focusing device may be used in connection with any kind of cameraprovided. with arbitrary fittings, for instance, finders, etc.

Having now described my invention what I claim and desire to secure byLetters Patent is:

1. In a device for focusing the lens of a photographic camera, imageproducing optical elements located at the ends of a baseline and imagedisplacing optical elements cooperating with said image producing elements, said image producing and image displacing optical elementsadjustable towards each other in rectilinear direction parallel to theaxis of the camera lens and adapted to produce coincident images of eachdistant object on proper adjusting of their distance and means foradjusting the objective of the photographic camera with relation to theimage plane of same in accordance with the adjustment of the imageproducing and. image displacing elements of the focusing device.

2. In a device for focusing the lens of a photographic camera, imageproducing optical elements located at the ends of a base line connectedto the photographic camera, image displacing optical elementscooperating with said image producing elements and connected to a partof the camera adjustable with relation to that part which is inconnection with said image producing elements, said image producingelements and said image displacing optical elements movable towards eachother in rectilinear direction and adapted to produce coincident imagesof any object the image of which is in focus in the camera.

3. In a device for focusing the lens of a photographic camera,reflectors with substantially spherical reflecting surfaces at the endsof a base line, said reflectors connected to the photographic camera,image displacing optical elements cooperating with said reflectors andconnected to a part of the camera adjustable with relation to that partwhich isin connection with the said reflectors, said reflectors beinglocated at the ends of the base-line and said image displacing opticalelements movable'towards each other in rectilinear direction and adaptedto produce coincident images of any object the image of which is infocus in the camera.

4. In a device for focusing the lens of a photographic camera,reflectors with substantially spherical reflecting surfaces at the endsof a base-line, the reflecting surfaces of said reflectors forming partof one single spherical surface the reflectors connected to thephotographic camera, image displacing optical elements cooperating withsaid re flectors and connected to a part of the camera adjustable withrelation to that part which is in connection with the said reflectors,said reflectors at the ends of the baseline and said image displacingoptical elements movable towards each other in rectilinear direction andadapted to produce coincident images of any object the image of which isin focus in the camera.

5. In a device for focusing the lens of a photographic camera,reflectors with substantially spherical reflecting surfaces at the endsof a base-line, said. reflectors connected to the sensitive layercarrying frame of the photographic camera, image displacing opticalelements cooperating with said reflectors and connected with theobjective of the camera, said reflectors and said image displacingelements movable towards each other in rectilinear direction and adaptedto produce coincident images of any object the image of which is infocus in the camera.

6. In a device for focusing the lens of a photographic camera, a pair ofreflectors, one at each end of a base-line, a second pair of reflectors,the reflectors of the said second pair arranged in an angle withrelation' to each other, one reflector of the first pair cooper atingwith one reflector of the second pair, the reflectors of each of the twopairs being in invariable position with relation to each other and thepairs movable towards each other in rectilinear direction and the onepair in connection with the objective of the camera and the other withthe image frame.

7. In a device for focusing the lens of a photographic camera, a pair ofreflectors, one

at each end of a base-line and connected to the image frame of thecamera, a second pair of reflectors and a pair of lenses connected tothe objective frame of the camera, the reflectors of the said secondpair arranged in an angle with relation to each other, one lens and onereflector of the second pair acting in cooperation with one reflector ofthe said first pair of reflectors and the pairs of reflectors movableeach as a whole towards each other in rectilinear direction.

In testimony whereof I have signed this specification in the presence oftwo subscribing witnesses.

WALTI-IER THORNER. WVitnesses HENRY HAsrER, WOLDEMAR I'IAUPT.

